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Bob McDavitt's ideas for sailing weather around the South pacific

27 February 2010

BOBGRAM7 issued 28 Feb 2010

WEATHERGRAM
YOTREPS
Issued 28 Feb 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TSUNAMI
The Tsunami ripples from that 8.8 Chilean quake seem to have mostly done
their dash now. If you are on Internet and are quick enough you can see
them at http://bit.ly/nzwaves . My condolences to anyone who suffered
from the quake and its waves, this planet can indeed be a rough place to
live at times.

TROPICS
SARAH started as a tropical depression with enough squally gales to
damage Penryhn Island in Northern Cooks early last week and has been
moving slowly south for much of last week until finally earning its name
a few days a go. It has now lost its top clouds and visible imagery
show a well-wound up compact spiral of cloud, slowly and erratically
looping. If it comes much further south it will likely get ripped apart
in an unfavourable environment. It still has gales and squalls but
these too should fade over Southern Cooks over next few days.

Computer models are picking another tropical low (or two) likely to form
near the south end of the main Islands of French Polynesia PF around 3
or 4 March UTC. This system should deepen as it moves south, so that
winds over PF are likely to be from the northwest for much of this week-
and squally.

A new pulse of extra tropical convection visited Northern Australia last
week and has culminated is a deep low over the mainland of Australia.
This system has too much friction and not enough access to sea-warmth so
is not expected to become a tropical cyclone, but is windy and wet
none-the-less and should spend this week heading south across central
Australia merging on the south-side over Melbourne on Thu 4 March with a
trough crossing the Australian Bight.

The South pacific Convergence zone has been concentrated near Northern
cooks for past week or sop, and scattered and disorganised elsewhere.
Well, this week it is likely to reform across the northern Coral Sea/
Solomons/Tuvalu/Samoa. In fact a tropical Low is expected to form on
the SPCZ and between Vanuatu and Fiji but Tue 2 March and then cross
Fiji on Wed 3 March and then drift south past Raoul Island on Fri 5
March, possibly getting close to northern NZ over the weekend of 6/7
March or early next week. This system isn't expected to become a
full-on cyclone but does deserve respect.

There is a good risk that another low may form near Vanuatu next week ,
8-12 March and that one may become a tropical cyclone, more about that
in my next weathergram.

SUBTROPICS

The subtropical ridge is strong and hugging 40S to 45S in the South
Pacific.

The High centre east of the North Island today, sun 28 Feb, should
steadily wander east this week along 40-45S reaching 120w by about sat
6 March, sort of a repeat of last week. AVOID the squash zone between
this High and that low over southern PF

The next HIGH should enter the central Tasman Sea on Wed 3 March and get
defected south across the South Island on Fri 5 March. AVOID the squash
zone between it and Low near Raoul Island or northern NZ on Sat 6 March.


NEW ZEALAND

Between the two Highs is a transitional trough. This one seems to have
missed (just/today) the opportunity to get an injection of energy from
the heat trough/monsoonal low over central Australia, so should cross NZ
on Tuesday 2 March, containing two fronts, first is preceded by NW winds
and second is followed by SW winds. There may be some heavy rain in the
west with the fronts. Winds are likely to turn S over the North Island
on Wed 3 March and SE/E for rest of week - with HIGH to south and Low to
north, a recipe for strong winds.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

21 February 2010

BOBGRAM7 issued 21 Feb 2010

WEATHERGRAM
YOTREPS
Issued 21 Feb 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
RENE has had its day, and now there is a concentration of South pacific
convergence zone convection in a line from Tuvalu to Tokelau to Northern
Cooks which seems to be most active near EQ 160W. A low has now formed
near 8S 160W., The EC model output suggests that this low move south
near the 160W line bothering the Cook Islands, reaching the Rarotonga
area around wed /Thu 24/25 Feb, and other model output suggest that
a/another development may form next week. .So if you are in the Cooks
keep tuned, if you have Internet then you can get the EC model at
http://bit.ly/ecoz but you'll have to select Southern Hemisphere to see
the Low/cyclone.. (the next name on the cyclone list is SARAH, but this
Low , at this stage, hasn't earned a name yet )


Elsewhere around the South Pacific there is just scattered unorganised
convection, but there may be a Tropical low over NW Australia this week
and there is a cyclone GELANE in the South Indian Ocean.


SUBTROPICS

The subtropical ridge is strong and hugging 35S to 40S in the South
Pacific.

The High centre east of the North island today , sun 21 Feb, should
steadily wander east and then fade when it reaches 35S 150W on Sat 27
Feb

The next HIGH should cross Bass Strait on Thu 25 Feb and then the
central Tasman Sea on Fri 26 Feb and central NZ on Sat 27 Feb=== third
anticyclonic weekend in a row for NZ.

North of these Highs there are well defined between 15S and 30S, and
occasionally there is a squash zone near 30S.

NEW ZEALAND

Between the two Highs is a transitional trough. It is bringing some
warm air from Australia, so temperature in the SE of the Si may soar to
30 C in the prefrontal gusty NW winds on Mon 22 Feb.

The low associated with this trough is likely to peak on Tuesday in the
South Tasman sea and its associated frontal band should bring heavy rain
to W of the South Island on Wed 24 Feb, then weaker rain to west of
North Island on Thu 24 Feb, followed by a southerly/southwest wind
change with showers for eastern areas on Friday 26 Feb

So it's a mediocre mid-week transition from one weekend BBQ High to
another J

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

13 February 2010

BOBGRAM7 issued 14 Feb 2010

WEATHERGRAM
YOTREPS
Issued 14 Feb 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

RENE seems to have maybe done a loop just east of Ta'u in eastern
American Samoa last night, and is now Cat 3 and may get to Cat 4
(170kph) ... heading for Ha'apai on local Monday morning and then may
travel across western side of Tongatapu Monday evening/night ... the
accompanying dangerous quadrant and storm surge will be o its
south-eastern side, so Nukualofa is in for a real battering. Brace.

RENE is likely to wander SW for a while longer but unravel as it leaves
the tropics and encounters cooler waters. There is a trough heading
east across the Tasman Sea ... it should cross New Zealand on
Wednesday/Thursday and pick up the remains of RENE and conduct them off
to the southeast on Friday and Saturday.

By then much of the rain will be east and south of its centre, so it
looks as though this rain may miss Northland (where it would be
welcome). However if RENE gets to travel a little faster than forecast
then maybe some of this rain will reach Northland. It's a race between
trough and RENE.

That trough spent last week delivering lots of welcome rain to the
interior of Australia as a low in the heat trough. the low is deepening
rapidly tonight of New South Wales as it encounters the EAC (East
Australian Current). The Low should weaken as it crosses the Tasman Sea
on Monday and Tuesday, fading back into a trough when it reaches the
South Island on Wednesday.

This Low seems to have missed out on the injection of cold air that I
mentioned last week - it has a protective ridge on its south-side.
However that ridge will have gone east of NZ by Wednesday and that's
when the new High is expected to be approaching Tasmania, throwing a
fresh dose of SW winds from the Southern Ocean ahead of itself--- if
this cold SW wind can get any where near the remnants of RENE then there
will be fireworks. At this stage this timing is against such an event,
and the High is expected to intervene and reach the North island by
Saturday ... maybe there will be an encounter well east of the North
Island on Friday/Saturday-maybe not.

Talking about fireworks: the South Pacific Convergence Zone SPCZ
remains very active along 5 to 10S across the South Pacific, especially
between Tokelau and Northern Cooks. Computers are picking a further
development in the area northeast of Samoa being born between Thursday
18 Feb and Tue 23 Feb (models are still differing on timing). The next
name on the Cyclone list is SARAH. Current output indicates this system
may move south sort of midway between Niue and Aitutaki/ Rarotonga -
however there is still plenty of time for it to take another path. Be
Aware.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

06 February 2010

BOBGRAM7 issued 7 Feb 2010

WEATHERGRAM
YOTREPS
Issued 7 Feb 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

The remains of TC OLI have crept off to the south of French Polynesia FP
now. During the coming week the South Pacific Convergence Zone SPCZ is
strong along 5 to 10S - with westerly winds on its northern side. Lows
are expected to be winding-up near Tokelau and Northern Cooks.

This coming weekend one of these systems mare deepen and widen a lot and
move WSW towards Samoa/Tonga /Fiji, and, next week, may be able to get
to New Caledonia area before heading south. There is still plenty of
time for this system to take another path, but basically if you do
intend sailing anywhere around the South Pacific between 10 and 20 Feb
check out this system first.


SUBTROPICS/NEW ZEALAND
How strange the subtropics are in their extremes. We are at the extreme
high point of summer now, and this weekend last year we had Black
Saturday and the tragic bushfires of Victoria; well: in the peak of
summer 2010, we are having extreme rain near Coffs Harbour - easing off
by Tuesday. One of causative factors is a sustained trade wind flow
along 25S all the way from south of FP top the NSW/QLD border -- I
remember a similar pattern in the South Pacific in Feb 1988, after I
returned to bench forecasting after the Americas Cup in Perth - and that
culminated in Cyclone BOLA - well this time is seems Coffs is copping it
rather than Gisborne, and there are no cyclones involved--- yet.

The High that is moving onto the South Island on Monday marks the South
Pacific subtropical ridge SPSR. This has been deflected to a latitude
south of its normal position over past few weeks by blocks in the upper
air - rather out-of-keeping with the current El Nino. High's path to
the east is blocked, and so this week it will drift north instead,
getting back to its normal position between Lord Howe and Raoul Islands
by Friday 12 Feb --- allowing El-Nino like NW to westerly winds to rage
and return to Southern NZ.

The next HIGH will build well south of the Aussie Bight, so stand by for
a cold southerly change over South Australia/Victoria/Tasmania on
Thursday/Friday /Saturday 11-13 Feb.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

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